1. Technical Field
The present invention relates to a liquid ejecting apparatus, and a liquid container of an ink jet printer or the like, and also to a method for determining the liquid level of the liquid container.
2. Related Art
An ink jet recording apparatus is a kind of known liquid ejecting apparatus that ejects liquid from a liquid ejecting head to a target. Hereafter, such devices may, without loss of generality, be referred to using the linguistically convenient term, “printer”. Printers are equipped with an ink cartridge (liquid container) for holding ink (liquid), and with a recording head (liquid ejecting head) for ejecting ink. Printers may execute printing operations in part by feeding pressurized air from a pressure pump through an air feed channel into the ink cartridge to pressurize an ink pack in the ink cartridge, thereby feeding ink to the recording head through an ink feed channel (liquid feed channel), and ejecting the ink from the nozzle of the recording head to a recording medium.
However, such printers have a disadvantage such that, if the pressure of the pressurized air that pressurizes the ink pack in the ink cartridge drops excessively while the pressure pump is at a standstill, sufficient ink is not fed to the recording head, causing problems in printing. To address this sort of problem, the printers described in JP-A-2001-212974 and JP-A-2001-253085 are configured to drive a pressure pump when a pressure sensor, disposed along the air feed channel serving as a pressure region, detects the lower limit of the pressure necessary for feeding ink from the ink cartridge to the recording head.
However, printers configured as described in the preceding paragraph have a problem such that, when the ink pack is about to run out of ink, a sufficient amount of ink necessary for printing is not supplied to the recording head even though the pressure pump is driven to apply pressure to the ink pack. To address this kind of problem, the printer described in JP-A-2002-154219 is equipped with a pressure sensor, in a pneumatic chamber serving as a pressure region in the ink cartridge, with which a difference, between the pressure of the pressurized air in the pneumatic chamber and the pressure of ink supplied from the ink pack to the recording head, is measured, thereby checking the ink level.
However, the printer described in JP-A-2002-154219 has low design flexibility because the location of the pressure sensor is limited to the boundary between the pressure region and the no pressure region in the ink cartridge. This is because the difference between the pressure of the pressurized air in the pneumatic chamber and the pressure of the ink supplied from the ink pack to the recording head, is measured. This reduced flexibility in design is a problem.